Technology: The mice that sprint through Denmark's sewage

The sewer systems of most European cities are frequently overwhelmed by the huge quantities of rainwater during storms. Treatment plants cannot cope, so the water is allowed to escape through outfalls into rivers. Although overflowing sewage is greatly diluted, it is still polluting.

Water companies can overcome this by enlarging sewers to act as temporary underground reservoirs. But researchers estimate that cities in the European Community may have to spend up to £80 billion improving sewers to prevent overflows. Now Danish engineers are putting the finishing touches to a computer system that monitors the weather to predict storm water and then controls sewage flows to make the best use of existing sewers.

The Danish city of Aalborg had predicted that to improve its sewer system it would need new storage tanks with a capacity of 10 000 cubic metres. But instead, engineers are commissioning a computerised system to control the ...

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